1. Field of the Invention
The present invention relates to a method for resizing a pattern to be written by lithography technique, and a charged particle beam writing method. More particularly, for example, the present invention relates to a method of previously resizing a pattern by using a dimension change amount of the pattern which is produced by a loading effect when performing a pattern forming after writing the pattern using electron beams, and to a writing method and apparatus for writing a pattern on a target workpiece based on resized pattern data using electron beams.
2. Description of the Related Art
Microlithography technology which forwards miniaturization of semiconductor devices is extremely important, because only this process performs forming a pattern in semiconductor manufacturing processes. In recent years, with an increase in high integration and large capacity of large-scale integrated circuits (LSI), a circuit line width required for semiconductor elements is becoming narrower and narrower. In order to form a desired circuit pattern on these semiconductor devices, a master pattern (also called a mask or a reticle) with high precision is required. Then, since the electron beam (EB) technology for writing or “drawing” a pattern has excellent resolution intrinsically, it is used for manufacturing such high precision master patterns.
FIG. 14 shows a schematic diagram describing operations of a conventional variable-shaped electron beam writing apparatus. The variable-shaped electron beam (VSB) pattern writing apparatus operates as follows: As shown in the figure, the pattern writing apparatus includes two aperture plates. A first or “upper” aperture plate 410 has an opening or “hole” 411 in the shape of a rectangle for shaping an electron beam 330. This shape of the rectangular opening may also be a square, a rhombus, a rhomboid, etc. A second or “lower” aperture plate 420 has a variable-shaped opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired rectangle. The electron beam 330 that left a charged particle source 430 and has passed through the opening 411 is deflected by a deflector. Then, the electron beam 330 passes through a part of the variable-shaped opening 421 of the second aperture plate 420, and irradiates a target workpiece 340 mounted on a stage that is continuously moving in a predetermined direction (e.g. X-axis direction). In other words, a rectangular shape capable of passing through both of the opening 411 and the variable-shaped opening 421 is written in a pattern writing region of the target workpiece 340 mounted on the stage. This method of writing or “forming” a given variable shape by letting beams pass through both of the opening 411 and the specially shaped opening 421 is called a variable shaped beam (VSB) system.
In the electron beam writing mentioned above, highly precise uniformity of the line width is required in the surface of a target workpiece, such as a mask surface, when writing a pattern on the target workpiece. However, in the electron beam writing, a phenomenon called a proximity effect occurs when electron beams irradiate a circuit pattern on a mask where resist is applied. The proximity effect is generated by the backward scattering of electron beams penetrating a resist film, reaching a layer thereunder to be reflected, and being incident into the resist film again. As a result, a dimension change deviated from a desired dimension occurs when a pattern is written. On the other hand, after writing a pattern, when developing the resist film or etching the layer thereunder, a dimension change called a loading effect caused by density difference of a circuit pattern occurs.
As the loading effect being a dimension change occurring in a charged particle beam writing represented by an electron beam writing, the following can be cited as examples: a loading effect generated when developing a resist film, a loading effect generated when etching chromium (Cr) serving as a shading film under a resist film, and a loading effect generated when a pattern dimension change is produced by chemical mechanical polishing (CMP). In the electron beam writing, more highly precise uniformity of the line width in a mask surface is required with narrowing the line width of a pattern. Therefore, a loading effect correction to correct the dimension change caused by the loading effect is needed. The correction is executed, based on a design line width of a circuit pattern (design pattern), by performing writing using a dimension resized by previously estimating a dimension change amount (dimension error) caused by a loading effect, and then a desired design line width can be obtained after the loading effect produced by etching etc. For example, when a calculated dimension change amount produced by a loading effect becomes positive (direction of the line width becoming wide), the circuit pattern is irradiated after being resized so that the line width may become narrower than the design line width by the dimension change amount produced by the loading effect.
As to the loading effect correction, it is disclosed that a pattern data correction amount is calculated by adding a loading effect correction amount for correcting a dimension change produced in etching, to a process resizing amount for correcting a pattern shape error generated in writing and developing. ((Refer to, e.g., Japanese Unexamined Patent Publication No. 2004-279950 (JP-A-2004-279950))
As the method of resizing a pattern for correcting the loading effect, there are a method of performing correction by changing a dose amount of electron beams after the shot division and a method of correcting the pattern shape itself before the shot division. The latter method will be described hereinafter.
Conventionally, when correcting a pattern shape itself, namely resizing a pattern dimension, a uniform resizing amount has been used for a pattern included in a certain small region regardless of the pattern shape. However, with an increase in miniaturization of a writing pattern, problems have occurred because of using a uniform correction amount (resizing amount) for all of a pattern. For example, in the case of a resizing amount being 20 nm, if a figure pattern with a width of 1 μm is resized to be narrower, the width becomes 980 nm and its reduction rate is 2%. On the other hand, if a figure pattern with a width of 100 nm is resized to be narrower, the width becomes 80 nm and its reduction rate is 20%. That is, an over-correction is made for the figure pattern with a width of 100 nm. Thus, when using a uniform resizing amount in a small region, the writing cannot be highly precisely executed because an over-corrected pattern is formed.